Lumber boards produced in a sawmill or the like frequently exhibit knots, knotholes, pitch pockets, excavations made by birds or insects or other defects that detract from the quality of the board. Knots are acceptable or even desirable for some purposes but problems can still arise from the presence of loose knots, split knots or knotholes. Some types of defect can also occur in other structural materials such as fiberboard for example.
The quality of such boards or the like can be upgraded by cutting out the defective area and filling the resulting opening with a plug which may, for example, be a conforming piece of wood or hardened wood paste or mastic material. Such plugs have typically been held in place solely by adhesives and this can itself be a source of problems. Such plugs can be loosened and ejected from the board by impacts or other forces.
Prior efforts to inhibit dislodging of the plug have typically involved complicated operations such as the cutting of openings and forming of matching plugs that have convoluted shapes designed to resist twisting of the plug or to provide a greater area for application of adhesive. While such measures are effective to a degree, retention of the plug remains basically dependent on the adhesive bond.
Applicant's above identified copending U.S. patent application Ser. No. 383,448 discloses a board repair which can be easily performed and in which the plug is positively interlocked into the body of the board. Forces applied against either of the opposing faces of the board cannot dislodge the plug.
Defects of the type which should be repaired can occur along the edges of the board in which case the plug can be susceptible to ejection by forces acting in a direction that is parallel to the plane of the board or the like. It would be advantageous, in the case of repairs to defects at the edges of the board, if the plug inherently resisted ejection by such forces in addition to resisting dislodging by forces acting in directions normal to the plane of the board.
The present invention is directed to overcoming one or more of the problems discussed above.